## Algebra and Trigonometry 10th Edition

$20 \leq x \leq 70 \\ y \geq 110-0.5 x \\ y \leq 187-0.85 x$
Let us suppose that $x$ is the age and $y$ is the heart rate. So, the age of the person will be: $20 \leq x \leq 70$ The minimum heart rate at $50 \%$ is $y \geq 0.5( 220-x)$ The maximum heart rate at $50 \%$ is $y \leq 0.85( 220-x)$ So, the system of inequalities is: $20 \leq x \leq 70 \\ y \geq 110-0.5 x \\ y \leq 187-0.85 x$